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PEG-PLA Nanocapsules Containing a Nanobiotechnological Complex of Polyhemoglobin-Tyrosinase for the Depletion of Tyrosine in Melanoma: Preparation and In Vitro Characterisation

Caroline Fustier and Thomas M.S. Chang

Poly (ethylene glycol)-poly (lactic acid) block-copolymer (PEG-PLA) was optimized and characterized using H-NMR spectrum and DSC thermogram. This was then used for the preparation of PEG-PLA nanocapsules containing polyhemoglobin-tyrosinase. Transmission electron microscopic and scanning electron microscopic studies showed round and non-aggregated nanocapsules with a PEG halo around each nanocapsule. Dynamic Light Scattering showed that the Z-average diameter was 65.2 ± 0.5 nm (mean ± SEM) and the polydispersity index was 0.262 ± 0.002. Factors controlling the diameters included the stirring speed of the reaction mixture and the size of the PLA block in the PEG-PLA copolymer. At the body temperature of 37ºC, free tyrosinase lost all its enzyme activity after 8 hours. However, Polyhemoglobin-tyrosinase nanocapcules retained 80% of its initial activity after 8 hours. This paper contains the first part of our work on the preparation and in vitro characterisation of PEG- PLA Polyhemoglobin-tyrosinase nanocapsules. Preliminary result in rats shows that 1 intravenous injection lowers the systemic tyrosine level to 10-13% after 5 minutes. The result of the detailed in vitro study and the preliminary animal study have led to our ongoing detailed animal research to be reported in subsequent papers.